In peritoneal dialysis (PD), a dialysis solution (dialysate) is introduced into the abdominal cavity of a patient. After a certain dwell time, during which an exchange between the dialysate and blood takes place via the peritoneum of the patient, the now “used” dialysate is replaced by fresh dialysate. For this purpose, the used dialysate usually is drained into a bag. During the dwell time in the abdominal cavity, the color of the dialysate changes. Besides a discoloration of the dialysate, turbidity can frequently be observed. Normally, the dialysate should have the color of apple juice. Upon being drained, the discoloration or turbidity of the used dialysate is subjected to a visual inspection by the physician, the person responsible for the dialysis or the patient himself. By means of the turbidity, it is evaluated whether the used dialysate has a usual, normal discoloration. If the discoloration is classified as being abnormal, further examinations usually are initiated to find out the causes. Discolorations which are not within the expected normal range can indicate various pathological causes, such as an increased secretion of protein, a secretion of blood, or they might for instance indicate early-stage peritonitis (inflammation of the peritoneum). In the case of unusual discolorations, it is recommendable to consult a physician in order to possibly initiate further examinations.
What is problematic in the visual inspection is the subjective perception of the observer, in particular of the untrained patient. Due to subjective and changing criteria for evaluation, the observer cannot always recognize with constant certainty whether the dialysate drained from the abdominal cavity exhibits a comparatively normal or abnormal discoloration.